[R] analogue of group option of SAS MIXED/random in R

[Bruno L. Giordano]

Dear list,

I am trying to use lme to build the analogue of the following SAS MIXED
random specification:

random int+Variable1+Variable2 /subject = Subject group=Condition type=vc;

which gives a Condition-blocked heterogeneity in the random effects
variance-covariance matrix.

Needless to say, I have a hard time in specifying Condition-specific
heterogeneities in the variance-covariance parameters.

I initially tried the following commands (without Condition-heterogeneity in
the random effects):

G.Data<-groupedData(Response~1|Subject,data=In.Data)
Fit1<-lme(Response~1+Variable1+Variable2*Condition,random=pdDiag(~1+Variable1+Variable2),method="REML",data=G.Data)

but have no idea about where to go from here (note that I don't want to nest 
Subject in Condition).

Thanks!!

    Bruno